Molecules such as nucleic acids, proteins, and lipids, molecular aggregates such as intracellular organelles and extracellular vesicles, and cells, which are derived from a living body, are analysis targets when mechanisms of a physiological phenomenon and a pathological phenomenon are explained and an effect at a time at which drug treatment is performed is quantitatively evaluated.
Generally, a plurality of different components such as molecules, molecular aggregates, particles, and cells are mixed in a sample extracted from a living body. Thus, it is necessary to separate/purify only a component serving as an analysis target. Physical properties such as a size, a specific gravity, a water/oil distribution coefficient, an isoelectric point, and a surface potential or molecule affinity (affinity) can be used as indexes when a component in a sample is separate/purified.
As a method for performing separation/purification using a surface potential, a free flow electrophoresis method is known (refer to Non-Patent Literature 1).
A free flow electrophoresis method is technology in which a voltage is applied to electrodes provided at both sides of a separation tank while a sample flows in the separation tank from an upstream side to a downstream side in a laminar flow shape together with a buffer solution such that an electric field is applied to a splitting tank in a direction perpendicular to a flow of the buffer solution, the sample is subject to free zone electrophoresis, and a component in the sample is separated using a difference between electrophoretic mobility of components in the sample.
According to a free flow electrophoresis method, components mixed in a sample can be separated/purified using a difference between surface potentials (electrophoretic mobility) of the components. Furthermore, a specific component can also be arbitrarily separated by bonding molecule tags having a specific affinity, such as antibodies, to components in the sample and using a change of the surface potential occurring as a result of the bonding of the antibodies to the components.
A free flow electrophoresis device in the related art is large and needs a large amount of a sample to separate components mixed in the sample, for example, extracellular vesicles such as exosomes (refer to Non-Patent Literature 2). Furthermore, the free flow electrophoresis device in the related art is expensive. In order to solve such problems, development research of a small-sized free flow electrophoresis device (a micro-free flow electrophoresis chip) to which micro-fluidic device technology is applied has been recently conducted. In addition, it is disclosed that a prototype small-sized free flow electrophoresis device is effective in separating a small amount of a sample (refer to Non-Patent Literature 3).
In a free flow electrophoresis device using micro-fluidic device technology, there are problems in that an influence of bubbles occurring on electrodes due to electrolysis is large and a stable operation for a long period of time may be difficult in some cases. In order to solve such problems, a method for separating a separation tank and an electrode tank using a gel with ion permeability and removing bubbles by refluxing a sample in an electrode tank without disturbing a laminar flow in the separation tank is suggested (refer to Non-Patent Literature 4).